Smoking was second only to chronological age in predicting fine wrinkling of photo-protected skin, reported Yolanda R. Helfrich, M.D., of the University of Michigan, and colleagues in the March issue of Archives of Dermatology.

Controlling for age, years of hormone therapy for women, years of smoking, and hours of lifetime sun exposure, the "optimal model" for predicting inner upper arm wrinkling included only chronological age (P<0.001) and packs of cigarettes smoked per day (P=0.04).

"Cigarette smoking has long been investigated as a risk factor for premature skin aging," the researchers said. However, the focus on research has been primarily facial wrinkling with no scales available to measure photo-protected skin, they added.

So they took standardized photographs of the inner upper arm skin of 38 men and 44 women who were patients at a dermatology clinic. They then picked five illustrating varying degrees of fine wrinkling on which basis three blinded judges scored the rest of the photographs twice, one year apart.

The 82 patients had a broad age range (11 with ages 22 to 29 years, 32 with ages 30 to 59 years, 27 with ages 60 to 79 years, and 12 with ages 80 to 91). Half had a history of smoking at some point in their lives ranging from 0.25 to 4.00 packs per day smoked.

The maximum interobserver variability one year later was 1.01 (P=0.30), and

The maximum intraobserver variability between grading periods was an average of 0.30Â±0.06, 0.62Â±0.08, and 0.47Â±0.10 for the three graders, respectively.

The predictive factors for skin aging were:

Chronological age (P<0.001),

Years of smoking (P<0.001),

Packs smoked per day (P<0.001),

Pack-years of smoking (P<0.001), and

In women, the number of births (P=0.004).

Inner upper arm wrinkling measured on the eight-point photonumeric scale described in the study was about two points higher among smokers than nonsmokers age 65 and older (P=0.004).

For those ages 45 to 65, fine wrinkles were about one point worse for smokers than nonsmokers (P=0.05).

While aging in photo-damaged skin may include roughness, coarse wrinkles, and pigment irregularities, aging in skin protected from the sun is predominantly characterized by fine wrinkles.

However, some of the underlying mechanisms may be the same for both, such as decreased collagen synthesis and increased matrix metalloproteinase (MMP) levels, the researchers said.

Aging of the skin by tobacco use "mirror those associated with UV light exposure," Dr. Helfrich and colleague wrote.

This suggests "that the generation of reactive oxygen species after tobacco exposure leads to molecular changes (elevated MMP levels and decreased levels of procollagen) that eventually lead to wrinkling and other changes we tend to associate with age, in photo-exposed and photo-protected sites," they added.

Racial and ethnic differences seen in photo-aged skin were not seen in photo-protected skin since there were not enough nonwhite participants in the study to detect a difference, the researchers said.

Further, larger studies may be needed to determine whether the photonumeric scale developed in the study could be used in nonwhite populations and to continue looking at risk factors for photo-protected skin aging, they added.

The study was supported in part by grants from the Babcock Endowment for Dermatologic Research and the National Institutes of Health. The researchers reported no financial disclosures.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco